Inspired by a mathematical riddle involving fuses, we define the "fusible numbers" as follows: $0$ is fusible, and whenever $x,y$ are fusible with $|y-x|<1$, number $(x+y+1)/2$ also fusible. We prove that set of numbers, ordered usual order on $\mathbb R$, well-ordered, type $\varepsilon_0$. Furthermore, density numbers along real line grows at an incredibly fast rate: Letting $g(n)$ be largest...